U.S. patent application number 14/212672 was filed with the patent office on 2014-09-18 for direct slurry weight sensor for well operation mixing process.
This patent application is currently assigned to Weatherford/Lamb, Inc.. The applicant listed for this patent is Weatherford/Lamb, Inc.. Invention is credited to Grant W. Ayo, Billy Williams.
Application Number | 20140269144 14/212672 |
Document ID | / |
Family ID | 50639977 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140269144 |
Kind Code |
A1 |
Ayo; Grant W. ; et
al. |
September 18, 2014 |
Direct Slurry Weight Sensor for Well Operation Mixing Process
Abstract
A slurry mixing system calculates a density of a slurry using
measured pressure differential and bulk velocity of the slurry.
Slurry from mixing of dry blend and mix fluid enters a one or more
tanks having agitators. A pump then pumps the slurry from the
tank(s) to the well, and a portion of the slurry is recirculating
back to a mixer. From the recirculated path, a direct slurry weight
sensor measures a pressure differential of the slurry between two
vertical measurement points of a known volume, and the sensor
measures a velocity of the recirculated slurry. Based on these
measures, the controller calculates a density of the slurry,
monitors a ratio of the dry blend and the mix fluid, and adjusts
the ratio based on the calculated density of the slurry if there is
a discrepancy.
Inventors: |
Ayo; Grant W.; (Magnolia,
TX) ; Williams; Billy; (Longview, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Weatherford/Lamb, Inc. |
Houston |
TX |
US |
|
|
Assignee: |
Weatherford/Lamb, Inc.
Houston
TX
|
Family ID: |
50639977 |
Appl. No.: |
14/212672 |
Filed: |
March 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61794150 |
Mar 15, 2013 |
|
|
|
Current U.S.
Class: |
366/8 ;
366/17 |
Current CPC
Class: |
B01F 3/1221 20130101;
B01F 15/0429 20130101; B01F 15/00233 20130101; B01F 15/0408
20130101; B01F 5/205 20130101; E21B 33/13 20130101; G05D 21/02
20130101; B01F 2003/1285 20130101; B01F 5/106 20130101 |
Class at
Publication: |
366/8 ;
366/17 |
International
Class: |
E21B 33/13 20060101
E21B033/13 |
Claims
1. A slurry mixing system of a well operation, comprising: a mixer
mixing a dry blend and a mix fluid into a slurry and delivering the
slurry for the well operation, a portion of the slurry being
recirculated back for mixing; a slurry sensor disposed in fluid
communication with the recirculated portion of the slurry, the
slurry sensor measuring a pressure differential of the slurry
between at least two vertical measurement points of a known volume;
and a controller operatively coupled to the slurry sensor, the
controller obtaining the measured pressure differential and
obtaining a velocity of the slurry, the controller calculating a
density of the slurry therefrom.
2. The system of claim 1, wherein the dry blend comprises a cement
or a fracing material, and wherein the mix fluid comprises
water.
3. The system of claim 1, wherein the mixer comprises at least one
jet supplying the mix fluid to the dry blend.
4. The system of claim 3, wherein the mixer comprises a pump
pumping the slurry for the well operation and recirculating the
portion of the slurry back to the at least one jet.
5. The system of claim 1, wherein the mixer comprises a pump
pumping the slurry for the well operation and recirculating the
portion of the slurry back for mixing.
6. The system of claim 5, wherein the mixer comprises at least one
tank; and wherein the pump discharges the recirculated portion of
the slurry to the at least one tank.
7. The system of claim 1, wherein the controller monitors a ratio
of the dry blend and the mix fluid delivered to the mixer and
adjusts the ratio based on the calculated density of the
slurry.
8. The system of claim 1, further comprising: a dry blend sensor
operatively coupled to the controller and measuring the dry blend
delivered to the mixer; and a fluid sensor operatively coupled to
the controller and measuring the mix fluid delivered to the
mixer.
9. The system of claim 1, wherein the mixer comprises at least one
tank having at least one agitator agitating the slurry.
10. The system of claim 9, wherein the at least one tank comprises:
a first tank mixing the slurry; and a second tank averaging the
slurry from the first tank.
11. The system of claim 1, further comprising a pump maintaining
the velocity of the recirculated slurry constant passing through
the slurry sensor.
12. The system of claim 1, wherein the slurry sensor comprises a
conduit arranged vertically and having the known volume between
first and second vertical locations as the at least two vertical
measurement points.
13. The system of claim 12, wherein the slurry sensor comprises
first and second pressure sensors sensing first and second
pressures for the pressure differential respectively at the first
and second vertical locations of the known volume.
14. The system of claim 13, wherein the first and second pressure
sensors each comprise: a sensing element for sensing pressure; a
diaphragm disposed at the vertical location and in communication
with the known volume; and a capillary communicating the sensing
element with the diaphragm.
15. The system of claim 1, wherein the slurry sensor comprises a
velocity sensor sensing the velocity of the recirculated
slurry.
16. The system of claim 1, wherein the slurry sensor comprise a
speed of sound sensor measuring a speed of sound in the slurry; and
wherein the controller determines volumetric phase fractions for
each phase in the slurry based on the pressure differential, the
velocity, and the speed of sound in the slurry.
17. A slurry mixing method of a well operation, comprising: mixing
a dry blend and a mix fluid into a slurry; delivering the slurry
for the well operation; recirculating a portion of the slurry for
mixing; measuring a pressure differential of the recirculated
slurry between at least two vertical measurement points of a known
volume; obtaining a velocity of the recirculated slurry; and
calculating a slurry density from the measured pressure
differential and the obtained velocity.
18. The method of claim 17, wherein the dry blend comprises a
cement or a fracing material, and wherein the mix fluid comprises
water.
19. The method of claim 17, wherein delivering the slurry for the
well operation comprises pumping the slurry.
20. The method of claim 17, further comprising: monitoring a ratio
of the dry blend and the mix fluid; and adjusting the ratio based
on the calculated slurry density.
21. The method of claim 17, wherein obtaining the velocity of the
recirculated slurry comprises maintaining the velocity of the
recirculated slurry constant passing through the known volume.
22. The method of claim 17, wherein measuring the pressure
differential comprises sensing first and second pressures for the
pressure differential respectively at first and second vertical
locations as the at least two measurement points of the known
volume.
23. The method of claim 17, wherein obtaining the velocity of the
recirculated slurry comprise measuring the velocity with a velocity
sensor.
24. The method of claim 17, further comprising: measuring a speed
of sound in the recirculated slurry; and determining volumetric
phase fractions for each phase in the recirculated slurry based on
the pressure differential, the velocity, and the speed of sound in
the recirculated slurry.
25. The method of claim 17, wherein recirculating the portion of
the slurry for remixing comprises recirculating the portion of the
slurry to at least one jet mixing the dry blend and the mix
fluid.
26. The method of claim 17, wherein recirculating the portion of
the slurry for remixing comprises recirculating the portion of the
slurry to at least one tank.
27. The method of claim 21, wherein maintaining the velocity of the
recirculated slurry constant passing through the known volume
comprises operating a pump feeding the recirculated slurry through
the known volume.
28. The system of claim 1, further comprising a pump feeding the
recirculated slurry through the known volume, wherein to obtain the
velocity, the controller operates the pump to maintain the velocity
of the recirculated slurry constant passing through the known
volume.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Appl. 61/794,150, filed 15-MAR-2013, which is incorporated herein
by reference in its entirety.
BACKGROUND
[0002] A number of industries use the flow of a slurry to achieve
various purposes. In the oil well industry, for example, a mixed
slurry of cement and water can be pumped downhole to support casing
and isolation zones of a formation. Operators can use many types of
cement mixers for these cement jobs, and the mixer can be designed
to handle the particulars of the slurry to be produced, including
water levels, additives, etc. Some typical mixers include jet-type
mixers, vortex mixers, and continuous recirculation mixers. In
other oil well applications, operators can pump a slurry of
treatment fluid downhole to treat or frac the formation in the
borehole. The slurry of treatment fluid can contain rock salt, wax
beads, proppant (e.g., sand, ceramic beads, etc.), benzoic acid
flakes, foam-based fluids, gelled and ungelled aqueous-based
fluids, or other kind of material used for treating or fracing a
formation. These applications can also use a mixer.
[0003] Successful cementing, fracing, and other slurry applications
rely a great deal on how the slurry is mixed and pumped for its
purposes. Therefore, a fundamental aspect of these operations
involves knowing and controlling the density of the slurry. (For
reference, cement slurry densities can range anywhere from about 7
lbm/gal [840 kg/m.sup.3] to about 23 lbm/gal [2760
kg/m.sup.3]).
[0004] In particular, oil well cementing operations require a
particular density that may need to change during the cementing
operation as different depths, downhole pressures, temperatures,
and formations call for slurries of different densities. Depending
on the application, the density of the slurry may also need to be
maintained within tight tolerance and may need to change quickly
during the operation. Moreover, the desired slurry may have a
particular complexity that proves hard to achieve. For example,
thixotropic slurries with very low "free water" requirements may be
needed for deep, high temperature-high pressure gas wells.
Therefore, the density of the slurry needs constant monitoring and
control at the wellsite during the cementing operation.
[0005] Although several technologies exist in the art for measuring
density of a slurry, current technologies used in mixing cement or
fracing slurries may not accurately measure the density of the
complex cement or fracing slurry. As one example, sensing
technologies can measure density using coriolis sensing or nuclear
sensing. Thus, one type of sensor used in measuring slurries is a
nuclear densitometer. Because it uses a nuclear source, the nuclear
densitometer imposes significant costs and restrictions on the
movement of the equipment, and special permits and handling are
required.
[0006] Even though the nuclear densitometer can be accurate,
operators can use a micro-motion coriolis sensor instead.
Unfortunately, coriolis technology loses accuracy as more air is
entrained or as particles of significantly different specific
gravity are utilized together in the slurry. Additionally, a
nuclear densitometer also loses accuracy as more air is entrained
and is dependent on characterizing the absorption of each slurry
material mix used.
[0007] Rather than using such sensors, an alternative approach in
the industry measures fluid rates on the input and output sides and
monitors the tub level to remain constant. This approach then back
calculates the solids in the slurry by determining the volumetric
difference of the slurry discharge rate and the base fluid supply
rate. Historically, either the density is interpolated, or several
mathematical assumptions are made to calculate density based on
average flow rate.
[0008] The subject matter of the present disclosure is directed to
overcoming, or at least reducing the effects of, one or more of the
problems set forth above.
SUMMARY
[0009] A direct slurry weight sensor, system, and method calculates
a density of a slurry using a measured pressure differential and a
bulk velocity of the slurry. Dry blend, such as cement or fracing
material, is delivered to a mixer, which then mixes a mix fluid,
such as water, with the dry blend. The resulting slurry enters a
mixing tank having an agitator to agitate the slurry. An averaging
tank with an agitator may also be used. Eventually, a pump pumps
the slurry from the tank(s) to the well, and a portion of the
slurry is recirculating back to the mixer for wetting the dry blend
and mixing with the dry blend and mix water.
[0010] A vertical conduit or pipe extends from the recirculated
path of the slurry and has a direct slurry weight sensor for
measuring properties of the recirculated slurry. In particular, the
sensor measures a pressure differential of the slurry between two
vertical measurement points of a known volume along the vertical
conduit. The sensor also measures a velocity of the recirculated
slurry. Based on these measures, the controller calculates a
density of the slurry.
[0011] As the mixing continues, a required density of the slurry
must be maintained and/or changed for the application at hand. For
example, too much mix water in a cement slurry reduces the strength
of the cement when it sets, and voids may form in the cement
column. Too little mix water in the cement slurry increases the
viscosity to the detriment of pumping, and voids of dry cement may
be present in the cement column.
[0012] Accordingly, the controller monitors a ratio of the dry
blend and the mix fluid delivered to the mixer and adjusts the
ratio if there is a discrepancy between the calculated density and
the required density for the application at hand. To monitor the
ratio, the system can have a dry blend sensor for measuring the dry
blend delivered to the mixer and can have a fluid sensor for
measuring the mix fluid delivered to the mixer. To measure bulk
velocity of the slurry, the sensor has a velocity sensor.
[0013] To measure the pressure differential, the system can have
separate pressure sensors sensing separate pressures at separate
vertical locations of the known volume on the vertical conduit.
Either one or both of these pressure sensors can have a sensing
element for sensing pressure, a diaphragm in communication with the
known volume, and a capillary communicating the sensing element
with the diaphragm.
[0014] Measuring fluid velocity and phase measurements are not the
direct intention of the system. Instead, the system seeks to
minimize the gas phase by measuring under an applied pressure to
the process fluid. The system then makes the velocity measurement
unnecessary by minimizing the distance between the sensor locations
and maintaining a constant velocity through the sensor. The
constant velocity can be maintained by a dedicated pump feeding
fluid to the density loop. On a cementing unit, there is a boost
pump and a recirculation pump that feeds the mixer. The system can
add a density recirculation pump.
[0015] The foregoing summary is not intended to summarize each
potential embodiment or every aspect of the present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 illustrates a mixing system according to the present
disclosure.
[0017] FIG. 2 illustrates a flow chart of a slurry mixing process
using the direct slurry weight sensor of the present
disclosure.
[0018] FIG. 3 schematically illustrates a direct slurry weight
sensor of the present disclosure.
[0019] FIG. 4 illustrates an embodiment of the direct slurry weight
sensor of the present disclosure.
DETAILED DESCRIPTION
[0020] A mixing system 10 in FIG. 1 delivers slurry for an
operation in a well 12. In this example, the mixing system 10
delivers a cement slurry for a cementing operation in the well 12,
but the teachings of the present disclosure can apply equally well
to other forms of slurring mixing, such as mixing slurries for
fracing or downhole treatment. Many of the components of the system
10 can be incorporated into a cementing skid or mixing truck, such
as commonly used at wellsites.
[0021] In the cementing operation shown, the system 10
pneumatically feeds bulk dry blend to an input of a recirculating
jet mixer 20 and uses a metering valve 24 or the like to control
the delivery of the dry blend into the mixer 20. At the same time,
the system 10 pumps mix fluid with a pump 30 into the mixer 20, and
a turbine flow meter 32 or the like measures the delivery of the
mix fluid. For cementing, the dry blend includes bulk dry cement
and any additives, such as loss circulation materials and weighting
materials, while the mix fluid is generally water. Other operations
would use other materials.
[0022] At the mixer 20, jets 22 spray the mix water at high
pressure into the mixer 20 to mix with the bulk dry cement
delivered pneumatically into the mixer 20. Additionally, a steady
stream of recirculated cement also enters the jet mixer 20 through
a port 26. This recirculated cement mixes with the freshly mixed
slurry of water and cement and helps wet the dry cement. The
resulting cement slurry exits the mixer 20 into a diffuser 28 and
drops into a mix tank 40, which has an agitator 42. The diffuser 28
can be a passive centrifugal air separator that helps separate the
bulk air used to convey the bulk cement and diffuses the energy of
the slurry entering the mix tank 40. As is known, air entrained in
the slurry can make accurate density measurements difficult.
[0023] From the mix tank 40, the slurry can flow to an averaging
tank 50, which also has an agitator 52. A pump 60 connected from
the tank 50 directs the slurry to the well 12 via a discharge
conduit 62. This pump 60 can be a high pressure pump, such as a
triplex positive displacement pump or the like. Output from the
pump 60 also diverts back to the mixer 20 through a recirculation
conduit 64. Diversion into the recirculation conduit 64 can be
controlled by a valve 63.
[0024] Further, a direct slurry weight sensor 100 is positioned
within a vertical conduit 66 extending from this recirculation
conduit 64. Diversion into this conduit 66 can also be controlled
by a valve 65. Slurry exits from this vertical conduit 66 into the
mix tank 40.
[0025] As noted below, a controller 70 uses readings from the
direct slurry weight sensor 100 to achieve a proper density at that
particular time during the cementing operation. The controller 70
has control electronics (i.e., microprocessor, memory, user
interface panel, etc.) and communicatively couples with the various
meters, valves, and sensors of the system 10 to automatically
control the mixing operations. Thus, the controller 70 connects to
the sensors 32, 100, and others, although these connections may not
be shown in FIG. 1.
[0026] As the system 10 operates, the controller 70 controls the
resulting density of the cement slurry being discharged by the pump
60 at particular times during the mixing process to meet the needs
for the cementing operation. Accordingly, the controller 70 can be
preprogrammed or automatically controlled with the appropriate
density and time data for the cementing process.
[0027] To control the resulting density of the cement slurry, the
controller 70 uses signals from the slurry weight sensor 100 and
signals from flow meters and controls of the cement metering valve
24 and/or the mix water sensor 32. Using these signals, the
controller 70 then adjusts the delivery of cement and mix water to
achieve the proper cement slurry density. The control depends on
the particulars of the cementing job, such as required density,
yield, water requirements, water specific gravity, etc., and the
controller 70 uses this information to calculate the delivery of
the dry bulk cement. Although not specifically detailed here, it
will be appreciated that the controller 70 controls various valves,
meters, and the like of the system 12 using hydraulics, electronic
signals, or other forms of activation known and used in the
art.
[0028] Measuring fluid velocity and phase measurements are not the
direct intention of the system 10. Instead, the system 10 seeks to
minimize the gas phase by measuring under an applied pressure to
the process fluid. The system 10 then makes the velocity
measurement unnecessary by minimizing the distance between the
sensor locations and maintaining a constant velocity through the
sensor 100. The constant velocity can be maintained by a dedicated
pump feeding fluid to the density loop. On a cementing unit, there
is a boost or recirculation pump 60 that feeds the mixer. In
addition to this arrangement, the disclosed system 10 can use a
density recirculation pump feeding fluid to the density loop. For
instance, a dedicated pump can be used on the recirculation loop,
such as at 67 on the conduit 66 or elsewhere. This dedicated pump
67 can be used to maintain a constant velocity of the recirculated
slurry passing through known volume and the sensor 100, thus
simplifying the monitoring and control by the controller 70 as the
system 10 operates.
[0029] As noted above, the direct slurry weight sensor 100 installs
in the recirculation loop. Rather than interpolating density or
making several mathematical assumptions to calculate density based
on average flow rate as historically done, the direct slurry weight
sensor 100 directly measures a weight of a known volume of the
slurry. Because the weight of the slurry is directly measured,
particle sizes and composition of the slurry do not adversely
affect the measurements, and only their weight contribution has
significance, which is the goal of the measurement.
[0030] As noted previously, the Coriolis technology loses accuracy
as more air is entrained or as particles of significantly different
specific gravity are utilized together in the slurry. Likewise, the
nuclear sensor loses accuracy as more air is entrained and is
dependent on characterizing the absorption of each slurry material
mix used. Such is not the case with the direct slurry weight sensor
100 of the present disclosure. As an additional advantage, the need
for a nuclear source sensor is eliminated, which enables the
equipment of the disclosed sensor 100 to be more mobile and less
regulated and reduces operating expenses.
[0031] The direct slurry weight sensor 100 operates as a flow meter
to directly measure the weight of a known vertical volume V of the
cement slurry. To do this, the sensor 100 measures a differential
pressure (P.sub.1-P.sub.2) between two measurement points
vertically displaced by a distance L, and the sensor 100 also
measures a bulk velocity of the slurry so that the slurry's density
can be calculated. The sensor 100 includes any suitable arrangement
of sensing elements to measure differential pressure and the bulk
velocity of the slurry, and these sensing elements can be
incorporated together into one or more packages or units used to
make the density measurement.
[0032] The direct slurry weight sensor 100 can also include another
sensor to measure the speed of sound in the mixture, which can be
used in determining the volumetric phase fractions for each phase
in the mixture based on the differential pressure, bulk velocity,
and speed of sound in the mixture. Overall, components of the
direct slurry weight sensor 100 can be similar to those disclosed
in commonly-owned U.S. Pat. No. 7,281,415, which is incorporated
herein by reference in its entirety.
[0033] Because the sensor 100 is arranged vertically along the
conduit 66, a small amount of pressure from the column of slurry is
applied to the sensor's volume. Thus, any minute amount of
entrained air in the slurry will be compressed in the volume, which
reduces its impact on the sample's volume. In this way, the
disclosed sensor 100 seeks to minimize one of the phases (i.e., any
gas phase in the slurry) so the disclosed sensor 100 can monitor
the density. Additionally, frictional pressure losses are
preferably reduced in the conduit 66 by minimizing the distance
between the sensing locations on the sensor 100. This can help
ensure that similar pressure is applied to all sensors, thus
removing this variable in the differential calculation.
[0034] Although the sensor 100 is shown disposed on the separate
conduit 66 from the recirculation conduit 64 and discharging to the
mix tank 40, the disclosed sensor 100 can be installed on a
vertical portion of the recirculation conduit 64, provided that the
sensor 100 does not restrict recirculation of the slurry.
Therefore, the separate conduit 66 may not be needed. Yet, the
separate conduit 66 may be preferred because the known volume for
the sensor 100 can be properly selected, the separate conduit 66
can be more readily arranged vertically, and flow into the separate
conduit 66 can be controlled by a valve 65 or the like.
[0035] Moreover, although the system 10 has the recirculation path
of the conduit 64 recirculate back to the mixer 20, this may not be
strictly necessary in some implementations. Instead, recirculation
may not be made to the mixer 20, and recirculated slurry may only
be communicated through vertical conduit 66 to the sensor 100 and
the mixer tank 40. As will be appreciated, these and other
alternative arrangements of the disclosed system 10 can be used for
a given implementation.
[0036] FIG. 2 shows a flow chart of a mixing process 200 using the
disclosed system (10) and direct slurry weight sensor (100). The
mixing process 200 as described here can pertain to mixing of a
cement slurry, but could apply equally to the mixing of other
slurries, such as fracing or downhole treatment slurries.
[0037] The controller (70) determines a desired slurry density
.rho..sub.o during the operation (Block 202). Depending on the
application, the desired slurry density .rho..sub.o can be dictated
by a number of factors, such as type of slurry, additives, depth,
downhole pressure, temperature, current zone of the formation, etc.
Delivery of the dry blend and the mix fluid is then set and
controlled to meet the desired slurry density .rho..sub.o (Block
204). For cementing operations, the dry blend includes the bulk dry
cement, and the mix fluid is typically water, but other operations
would use other materials.
[0038] As the mixing proceeds, the controller (70) monitors the
ratio of dry blend and mix fluid for the slurry (Block 206) and
monitors the pumping rate and other factors for desired delivery of
the slurry (Block 208). Adjusting the ratio of dry blend and mix
fluid primarily controls the slurry's density. If the feed of the
dry blend is constant and the feed of mix fluid is too low, then
the density of the slurry would be too high. This may result in an
insufficient volume of slurry delivered to the well. Additionally,
the slurry's viscosity would be too high so that excessive pumping
pressures may cause a loss of circulation. The reverse would be the
case if the feed of the mix fluid is too high compared to the dry
blend's feed.
[0039] As the operation proceeds, a portion of the resulting slurry
recirculates back to the vertical conduit (66) off the
recirculation conduit (64). As the diverted slurry flows past the
known volume V of the direct slurry weight sensor (100), the
controller (70) obtains the measured pressures P.sub.1 and P.sub.2
and the bulk velocity .nu..sub.slurry of the slurry from the direct
slurry weight sensor (100) (Block 210). The measured data can be
obtained at any desirable interval and can be communicated in any
of a number of ways to the controller (70).
[0040] Using the measured data and the equations noted below, the
controller (70) then calculates the average density
.rho..sub.slurry of the slurry (Block 212). Again, this calculation
can be performed at any desirable interval suited for controlling
the operation. The controller (70) then compares the calculated
average density .rho..sub.slurry to the desired slurry density
.rho..sub.o and determines if a discrepancy exits (Decision 214).
(Any perceived discrepancy may be based on a suitable threshold for
the type of slurry and the density levels involved). If a
significant discrepancy exists, then the controller (70) adjusts
the ratio of the dry blend and the mix fluid (Block 216). Of
course, the controller (70) also continuously monitors other
sensors, flow meters, pumps, etc. in the system (10) and makes
appropriate adjustments to pump rates, valves, etc. to control the
mixing process.
[0041] FIG. 3 shows one exemplary embodiment of the direct slurry
weight sensor 100 having one sensor arrangement for measuring
differential pressure and bulk velocity as well as the optional
speed of sound of the slurry. As shown, the sensor 100 installs on
a pipe or conduit 110 having flanges. This pipe 110 disposes
vertically along the vertical conduit (66) extending from the
recirculation conduit (64) of the disclosed system (10). (See FIG.
1).
[0042] In the arrangement of FIG. 3, the sensor 100 includes two
pressure sensors 104 and 106 disposed on the pipe 110 and displaced
vertically by a displacement L. These sensors 104 and 106 measure
the slurry's pressure at two measurement points on the pipe 110 so
a differential pressure (P.sub.1-P.sub.2) can be determined. The
vertical displacement L corresponds to the vertical distance
between the sensors 104 and 106 on the pipe 110, although the
vertical displacement may be trigonometrically determined if the
pipe 110 is not strictly vertical. In general, the displacement L
is chosen to provide a hydrostatic pressure difference large enough
to overcome accuracy and resolution limitations of the pressure
sensors 104 and 106.
[0043] The direct slurry weight sensor 100 also includes a sensor
103 for measuring bulk velocity (.nu..sub.mix) and a sensor 105 for
measuring speed of sound (.alpha..sub.mix) of the slurry. As
illustrated, the sensors 103 and 105 can be integrated into a
single assembly 102. A temperature sensor 107 may also be provided
to measure temperature, which can be used for variables of interest
that depend on temperature. For example, the speed of sound and
density variables are functions of temperature and pressure, which
may be determined based on measurements from the pressure sensor
106 and the temperature sensor 107. The sensor 100 can also have
other arrangements of these sensor elements at different locations
along the pipe 110 and the flow of the slurry.
[0044] As slurry flows vertically up the pipe 110, the pressure
sensors 104 and 106 measure the pressure differential of the slurry
between the measurement points. The velocity sensor 103 also
measures the bulk velocity of the slurry flowing through the pipe
110, and the speed of sound sensor 105 can measure the speed of
sound in the slurry. Temperature may also be measured by the
temperature sensor 107. The measurements from these sensors 103-107
are used by the controller (70; FIG. 1) to calculate the density of
the slurry as well as other desirable variables.
[0045] The pressure sensors 104 and 106 can be any suitable type of
pressure sensor, such as strain sensors, quartz sensors,
piezoelectric sensors, etc. The pressure sensors 104 and 106 can
also be fiber optic sensors using strain-sensitive Bragg gratings,
such disclosed in U.S. Pat. No. 5,892,860, which is incorporated
herein by reference. The velocity sensor 103 can be similar to
those described in commonly-owned U.S. Pat. No. 6,463,813, which is
incorporated herein by reference. Finally, the velocity sensor 103
and speed of sound sensor 105 may be similar to those described in
commonly-owned U.S. Pat. No. 6,354,147, which is incorporated
herein by reference. These and other types of sensors known and
used in the art can be used.
[0046] FIG. 4 shows an installation of the direct slurry weight
sensor 100. Here, the sensor 100 has a main sensing unit 120
coupled to a pipe 110 with a bracket 122. This pipe 110 has flanges
and couples to the vertical conduit (66; FIG. 1) of the disclosed
system. The sensing unit 120 houses the various pressure, bulk
velocity, and speed of sound sensors noted herein. Diaphragm seals
130 and 140 disposed on the pipe 110 are exposed to the pipe's
known volume between measurement points separated by vertical
displacement L. Thus, the pipe's known volume is characterized as
(V=.pi.r.sup.2L). Capillary tubes 132 and 142 extend from the
diaphragm seals 130 and 140 to the pressure sensing elements (not
shown) housed in the sensing unit 120. A transmitter 125 on the
unit 120 can transmit measured data to the controller (70; FIG. 1)
for processing.
[0047] With any of the sensor arrangements of FIGS. 3-4, the
controller 70 determines a density of the slurry passing through
the pipe 110 based on the differential pressure and the bulk
velocity of the slurry measured by the sensor 100. If desired,
volumetric phase fractions may also be determined based on the
determined slurry density and measured speed of sound in the
slurry.
[0048] Looking at the arrangement of FIG. 4, for example, the
density (.rho..sub.slurry) of the slurry is calculated using the
measured differential pressure (.DELTA.p) between P.sub.1 and
P.sub.2, and the measured bulk velocity (.nu..sub.mix) of the
slurry in the pipe's known volume (V=.pi.r.sup.2L). The average
density (.rho..sub.slurry) can be calculated using the following
equation:
.rho. slurry = p 1 - p 2 gh + Lfv slurry 2 4 r ##EQU00001##
[0049] As the cementing operation proceeds, the controller 70
calculates this slurry density (.rho..sub.slurry) and uses it to
control the density of the cement slurry being output by the system
(10) according to the desired results as disclosed previously.
[0050] Notably, the average slurry density (.rho..sub.slurry) may
be determined independent of the magnitude of slippage between the
different individual phases of the slurry in the pipe 110. In the
equation, the differential pressure (P.sub.1-P.sub.2) as well as
the bulk velocity .nu..sub.mix are measured using the sensor 100.
Frictional pressure loss is estimated using the measured bulk
velocity of the mixture and a well-known frictional loss equation
in which L is the length between the two measurement points, f is
the friction factor (e.g., a Moody friction factor calculated using
known roughness of an inner surface of the pipe, etc.), and r is
the inner radius of the pipe 110.
[0051] Because the sensor 100 is arranged vertically (or at least
approximately), a small amount of pressure is applied to the
sensor's volume due to gravity so any minute amount of entrained
air will be compressed in the volume. This can reduce the entrained
air's impact on the sample volume and calculations. Moreover,
minimizing the displacement L between the sensing locations on the
sensor 100 can reduce frictional pressure losses and help ensure
the same process pressure is applied to all sensors, thus removing
this variable in the differential calculation.
[0052] If desired, the volumetric phase fraction can also be
calculated. To determine this, the controller 70 measures pressure
and temperature of the slurry and calculates the density
.rho..sub.calc and speed of sound .alpha..sub.calc for each phase
using the measured pressure and temperature. After calculating the
average density .rho..sub.slurry with the previous equation from
the measured pressure differential (P.sub.1-P.sub.2) and bulk
velocity .nu..sub.slurry, the controller 70 can calculate the
volumetric phase fractions for each phase using the equation's
density P.sub.slurry and measured speed of sound .alpha..sub.slurry
and using the calculated density .rho..sub.calc and speed of sound
.alpha..sub.calc for each phase.
[0053] As noted previously, the techniques of the present
disclosure seek to minimize one of the phases, namely any air in
the slurry. Therefore, calculating the volumetric phase fraction
for gas (i.e., air) in the slurry can be used to verify that as
little air as possible is entrained in the slurry or for other
purposes. Equations for calculating the volumetric phase fractions
are disclosed in the incorporated U.S. Pat. No. 7,281,415, which
can be modified for the particular slurry of interest.
[0054] The foregoing description of preferred and other embodiments
is not intended to limit or restrict the scope or applicability of
the inventive concepts conceived of by the Applicants. In exchange
for disclosing the inventive concepts contained herein, the
Applicants desire all patent rights afforded by the appended
claims. Therefore, it is intended that the appended claims include
all modifications and alterations to the full extent that they come
within the scope of the following claims or the equivalents
thereof.
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